Man-made VLF whistler mode (WM) waves are employed in controlled experiments on wave growth and triggering within the magnetosphere. In one such experiment, VLF pulses of 1-s duration are interrupted by a 10-ms gap. Two types of gap are employed. In the first, the phase of the wave following the gap is the same as that of a constant-frequency wave with no gap. In the second type, this phase is reversed. The data indicate that the growth rate and saturation level of the postgap section of a pulse are independent of the phase shift introduced in the gap. Moreover, it is often observed that rising frequency emissions are triggered during the 10-ms gap. They closely resemble those emissions that frequently appear neear the ends of constant-freauency signals. The gap induced emissions may then interact with the postgap signals. Suppressions and entrainments between those signals are often observed. An explanation of the phenomenon of gap-induced emissions is based on the hypothesis that the radiation from the wave-organized electrons can switch from a 'forced' mode to a 'natural' mode after termination of the triggering wave. An experiment on the relation between gap length and the development of falling emissions confirms an earlier observation that falling emissions always start with a small rise in frequency. It also shows that a potsgap signal can 'capture' a gap-induced falling emission when its frequency is close to that of the postgap signal at its beginning.